With the expansion of the Digital Subscriber Line Access Multiplexer (DSLAM) network, it is necessary to select subscriber lines quickly, to locate faults accurately, and to maintain the lines automatically and periodically in the DSLAM network application.
As defined by the ITU-T ADSL2 (G.992.3), Dual-ended Line Testing (DELT) is a technology for testing the state of a line by setting test points at both sides of the line. The DELT technology is applicable to the test of the line diagnosis mode. The test data derived from a DSL test performed through the DELT technology helps a maintenance engineer analyze and find the location of the fault caused by crosstalk, radio frequency interference, or a (bridge) tap to discover the fault source.
DELT may measure the line attenuation directly to obtain the length of the measured line. The methods for obtaining the line length through the DELT technology include attenuation measurement, and frequency/phase measurement. For example, to measure the length of a downstream line, a DSL transceiver at the central office may insert an excitation signal into the line, and the DSL transceiver in the subscriber-end device may measure the frequency response. The line length is then calculated according to the received result of the frequency response. In another example, the line length may be calculated by testing the line attenuation.
The DELT technology for measuring the line length in the related art could be improved upon in the following areas:
(1) If the line diameter is unknown, the simple attenuation and frequency/phase tests do not produce a precisely measured line length.
(2) The test objects are unitary. For example, the related DELT technology provides no method for calculating a line diameter.